I've tried to bookmark all the sites in my categories that are/were hosted by GeoCities. I've already made an attempt to remove any that are down. Whenever I sign on to edit, I search the major SEs to see if I can "locate" any sites that have changed hosts. (My categories are mostly by real people using their real, individual names, so it's pretty easy to do.) Any sites that remain on my watchlist for an extended period (albeit arbitrary) without being "relocated" by search will be dropped altogether.
And as Windharp said, the automated processes are helpful in keeping up.